1. Field of the Invention
The present invention relates to a method for deinking printed waste paper using a peroxidase in the presence of a peroxide as the deinking agent. In accordance with the preferred embodiment of the invention, the enzyme is soybean peroxidase.
2. Description of the Prior Art
The recycling and use of waste paper has been dramatically influenced in recent years by public presence and by existing and pending government legislation. With the utilization of waste paper expected to continually increase in the future, the recycling of waste paper is believed to be one of the main issues facing the paper industry in the next decade and beyond.
Waste paper is most often used in the production of lower quality commodity grades such as linerboard, newsprint, etc. Recent advances in recycling technology, particularly, with respect to the deinking of printed waste papers allows the recycled pulp to be used in the production of higher grades of paper such as bond paper, etc. In the past, most papers were printed using primarily water or oil-based inks which are satisfactorily removed by conventional deinking methods which includes forming an aqueous pulp and contacting the pulp with a surfactant. The ink is separated from the pulp fiber and the ink is then subsequently removed by washing or floatation procedures. For example, the use of a substituted oxyethylene glycol nonionic surfactant along with a low molecular weight polyelectrolyte for deinking secondary fiber is described in U.S. Pat. No. 4,599,190 to Maloney. Betscher, U.S. Pat. No. 5,094,716 describes an improvement in the process for deinking groundwood newsprint wherein a combination of certain anionic surfactants in conjunction with a defoamer and a naphthalene-formaldehyde condensate is employed. Oil-based inks are generally saponified or dispersed under alkaline conditions and are thus broken up releasing the ink which can then be easily removed by any satisfactory means. There is, however, an increased use of electrostatic inks employed in printed matter such as xerography, etc. and these inks are much more difficult to remove than the common water or oil-based inks. As a result, waste paper produced from electrostatic ink-printed paper has a higher dirt count making for a lower grade product.
The removal of electrostatic inks and toners from xerographically printed waste paper has been described for example in U.S. Pat. No. 4,561,733 to Wood, U.S. Pat. No. 4,276,118 to Quick; U.S. Pat. No. 4,820,379 and U.S. Pat. No. 5,102,500 both to Darlington. While such attempts have been successful in removing most of the electrostatic inks or toners, generally some large agglomerates remain in the processed fiber giving it an undesirable appearance, particularly, when used in high quality paper.
Enzymes have been used in the treatment of paper pulps and for purifying the waste water effluents from paper mill operations. According to a 1991 article, "Enzyme Technology for Fiber Treatment" by T. W. Jefferies of the Institute for Microbial and Biochemistry Technology, USDA Forest products, Madison, Wis., lipases are presently being applied to pitch removal and deinking in lignocellulose bioprocesses. Japanese Pat. Nos. JP 2160984 and JP 2080684 describe the use of the enzyme, lipase, in the hydrolysis of soya-based inks. This enzyme, however, has no apparent effect on mineral-based inks. Another enzyme, cellulase, has been described in Japanese patent No. JP 2080683 where cellulase in combination with a surfactant may improve certain deinking processes. It is anticipated that such deinking would be advantageous in processes where fibers other than cellulosic fibers are used since it is known that cellulase is likely to damage cellulose fibers. European patent application No. EP 447672 describes deinking waste paper using a lignolytic enzyme. According to the European application, oxidation potential of the enzyme is critical to the deinking process.